1. Field of the Invention
This invention relates to a method for discharge of a liquid wished to be discharged and a liquid discharge head which resort to generation of bubbles by means of thermal energy, for example, and more particularly to a method for the discharge of a liquid and a liquid discharge head which rely on the use of a movable separation membrane capable of effecting displacement of its own in consequence of the generation of bubbles.
The term "record" as used herein means not merely the action of imparting images such as characters and figures which have meanings to a recording medium but also the action of imparting figures such as patterns which are destitute of meaning to the recording medium.
2. Related Background Art
The so-called bubble jet recording medium, i.e. the version of ink jet recording method which effects the formation of an image on a recording medium by exerting the energy of heat, for example, on an ink thereby causing the ink to produce a change of state accompanied by an abrupt volumetric change (generation of bubbles) and thereby enabling the force of action due to this change of state to discharge the ink through a discharge port and allowing the discharged ink to adhere to the recording medium, has been heretofore known to the art. The recording device which utilizes this bubble jet recording method, as disclosed in JP-B-61-59911 and JP-B-61-59914, is generally furnished with a discharge port for allowing the discharge of ink, an ink flow path communicating with the discharge port, and a heating element (electrothermal converting element) disposed in the ink flow path and adapted as an energy generating means for effecting the discharge of ink.
The recording method described above enjoys many fine features such as permitting easy production of recorded images and further color images of high resolution by the use of a small device because this recording method enables images of high quality to be recorded at high speed with low noise and the head embodying this recording method permits discharge ports for the discharge of this ink to be disposed in high density. The bubble jet recording method, therefore, has come to be utilized in recent years in numerous office devices such as printers, copying devices, and facsimile devices. It is now on the verge of finding utility in industrial applications such as for a printing device.
In the conventional bubble jet recording method, since the heating element held in contact with the ink repeats application of heat to the ink, it has the possibility of scorching the ink and forming on the surface thereof a deposit of scorched ink. When the liquid wished to be discharged is apt to be deteriorated by heat or it is not easily allowed to foam sufficiently, there are times when the formation of bubbles by direct heating with the heating element mentioned above will fail to bring about perfect discharge of the liquid.
The present applicant has proposed in JP-A-55-81172 a method for effecting discharge of a discharging liquid by foaming the bubble generating liquid with a thermal energy applied thereto through the medium of a flexible membrane adapted to separate the bubble generating liquid and the discharging liquid. This method is constructed such that the flexible membrane and the bubble generating liquid are disposed in part of a nozzle. In contrast, a construction using a large membrane capable of separating the head in its entirety into an upper and a lower part is disclosed in JP-A-59-26270. This large membrane is aimed at enabling a liquid flow path to be interposed between two plate members and consequently preventing liquids held back by the two plate members from mingling with each other.
As ideas that take consideration of foaming properties which are characteristic of bubble generating liquids themselves, an invention of JP-A-05-229122 which uses a liquid having a lower boiling point than a discharging liquid and an invention of JP-A-04-329148 which uses an electroconductive liquid as a bubble generating liquid have been also known to the art.
The conventional method for discharge of liquid by the use of a separation membrane has not reached a level of feasibility because it is constructed solely for the separation of a bubble generating liquid and a discharging liquid or is intended only for improving the bubble generating liquid itself.
The present inventors have pursued a study on the discharge of liquid drops by the use of a separator, with emphasis on the liquid drops subjected to discharging, and have consequently reached a conclusion that the discharge of liquid brought about by the formation of bubbles with the thermal energy has the efficiency thereof degraded through the intervention of the aging of the separation membrane and has not yet been reduced to practice.
The present inventors, therefore, have initiated a study in search of a method for discharge of liquid and a device therefor which can utilize the effect the function of separation by the separation membrane and meanwhile exalt the discharge of liquid to a higher level. The present invention has originated in the course of this study and is directed to providing an epochal method of discharge and a device therefor which can improve the efficiency of discharge of liquid drops and can stabilize and exalt the volume of liquid drops to be discharged and the speed of discharge of liquid drops. Specifically, this invention resides in a liquid charge head furnished with a first flow path used for a discharging liquid and adapted to communicate with a discharge port, a second flow path adapted to supply or transfer a bubble generating liquid and embrace a bubble generating region, and a movable separation membrane for separating the first and the second flow path, which features the ability to improve the efficiency of discharge.
The present inventors, particularly concerning the liquid discharge head disclosed in JP-A-5-229122, have demonstrated that a small empty space destined to serve as a bubble generating region is disposed on the upstream side of a discharge port relative to the direction of the flow of a discharging liquid, that the bubble generating region itself barely has the same width and length as a heating element, that when the bubble generating region emits bubbles, a flexible membrane is displaced by the generation of the bubbles only in the vertical direction relative to the direction of discharge of the discharging liquid, and that the liquid discharge head consequently entails the problem of producing no sufficient discharging speed and performing no efficient discharging motion. The inventors, regarding the cause for this problem, have taken notice of the fact that the same bubble generating liquid always uses repeatedly the closed small empty space and have ultimately realized the production of an efficient discharging motion by virtue of the present invention.
The present invention has been produced in the light of the problem encountered by the prior art as mentioned above. The first object of this invention is to provide, in a construction for substantially separating, preferably perfectly separating, a discharging liquid and a bubble generating liquid by means of a movable separation membrane, a method for the discharge of liquid and a liquid discharge head which, while the force generated by the pressure of bubbles is deforming the movable separation membrane and transferring the pressure to the discharging liquid, not only prevent the pressure from escaping toward the upstream side but also guide the pressure in the direction of the discharge port and give rise to a high discharging force without a sacrifice of the efficiency of discharging. The second object of this invention is to provide a method for the discharge of liquid and a liquid discharge head which, owing to the construction described above, allow a decrease in the amount of a deposit suffered to pile on a heating element and permit efficient discharge of liquid without inflicting a thermal effect on the discharging liquid. The third object of this invention is to provide a method for the discharge of liquid and a liquid discharge head which enjoy broad freedom of selection without reference to the viscosity of the discharging liquid or the composition of the material thereof.
Specifically, the major object of this invention resides in providing a method for the discharge of liquid and a liquid discharge head which, besides fulfilling the objects mentioned above, repress the vibration of the movable separation membrane during the extinction of bubbles, effect stable discharge, promote supply of liquid, and improve the property of refilling.